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4GuysFromRolla.com : ASP FAQS : The Nature of Things


Question:

How can I make inheritable classes in ASP?


[Print this FAQ]

Answer: Inheritance is an Object-Oriented concept that means that a class can get (inherit) part of it's definition from a more abstract parent class. See Using Object-Orientation in ASP.NET : Overview for a great overview of what it will mean in the upcoming ASP.NET release from Microsoft.

For current ASP, inheritance is really a function of the language you use to write pages with. Of the two supplied languages, VBScript and JScript, neither really supports inheritable classes, however JScript does come closer that VBScript. (One side note, if you build COM objects in VJ++ or VC++, inheritance will certainly be available to you. Also, you can directly use Java-based objects in your ASP, see An Introduction to using Java with ASP for more information.)

JScript objects can support a sort of inheritance. Say we have a class called CEmployee:

// Method of CEmployee class
function load(Name, DateOfEmploy, Title) {
    this.Name = Name;
    this.DateOfEmploy = DateOfEmploy;
    this.Title = Title;
}

function CEmployee(Name, DateOfEmploy, Title) {
    // Properties:
    this.Name = new String();
    this.DateOfEmploy = new Date();
    this.Title = new String();
    this.FireDate = new Date();
    // Methods:
    this.load = load;
    // Action on instantiation:
    this.load(Name, DateOfEmploy, Title);
}

It has a method called load and 4 properties. To use it from VBScript you need a a JScript function to access it:

function Employee(Name, DateOfHire, Title) {
    return new CEmployee(Name, DateOfHire, Title);
}

And can be used like so:

Dim objEmployee
Set objEmployee = Employee("Smith, John", "10/11/200", "Programmer")

Now say we want to create a class to represent a manager. Managers are also employees, but may have other properties and methods that make them slightly more than a mere employee. First define the new stuff for a manager:

function CManager(Name, DateOfEmploy, Title) {
// Secretary is a child CEmployee object: (or could be a collection)
    this.Secretary = new CEmployee();
// Action on instantiation:
    this.load(Name, DateOfEmploy, Title);
}

The CManager class gains a Secretary property (which is an employee object in this case). Then the apply the CEmployee's class to the CManager:

// CManager 'extends' CEmployee:
CManager.prototype = new CEmployee();

Add the same 'wrapper' function so VBScript can use CManager:

function Manager(Name, DateOfHire, Title) {
    return new CManager(Name, DateOfHire, Title);
}

And call it all from VBScript:

<%
Dim objManager
Set objManager = Manager("Ned Flanders", "12/12/1999", "Vice-President")

Dim objEmployee
Set objEmployee = Employee("Smith, John", "10/11/200", "Programmer")

' Set manager's secretary to an employee object:
Set objManager.Secretary = objEmployee

Response.Write "In VBScript:<br>"
Response.Write objManager.Title & " " & _
                            objManager.Name & "<br>Secretary:" & _
                            objManager.Secretary.Name
%>


FAQ posted by Richard Lowe at 12/13/2000 2:25:37 PM to the The Nature of Things category. This FAQ has been viewed 42,515 times.

Do you have a FAQ you'd like to suggest? Suggestions? Comments? If so, send it in! Also, if you'd like to be a FAQ Admin (creating/editing FAQs), let me know! If you are looking for other FAQs, be sure to check out the 4Guys FAQ and Commonly Asked Messageboard Questions!

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Last computed at 9/17/2007 3:22:00 AM


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